High and low clouds, stratus, fog

South of the North Sea. On the visible image, a strip of clouds (1) appears along England. The sky is clear elsewhere over the sea, except a small crescent of clouds (2). On the infrared image, the strip of clouds (3) along England is not as visible. It's only slightly clearer than the sea. The temperature of the top of these clouds is not much colder than the temperature of the sea. This means that they are low clouds, probably stratus clouds or even fog. On the other hand, the small crescent of clouds (4) appears definitely whiter than the sea, they are thus higher clouds.